Recent results have indicated that galactosyl transferase is the molecular constituent on rat liver plasma membrane which binds asialo-fetuin, thus initiating the hepactic uptake of this modified glycoprotein. To further show the involvement of galactosyl transferase in this process, asialo-fetuin will be chemically linked to Sepharose in order to make an affinity column for the membrane galactosyl transferase. Calcium ions are required for the binding, and it is expected that upon their removal from the eluting buffer, the galactosyl transferase will be released from the affinity column. Liver alpha-mannosidase is being purified in order to determine its ability to cleave alpha-D-mannosidic residue present on a fetuin modified by prior removal of sialic acid, galactose, and N-acetylglucosamine from the non-reducing ends of its carbohydrate chains. Recent literature results describe a lysosomal storage disease in which alpha-mannosidase is lacking, and patients with this disorder excrete excessive quantities of an alpha-mannosyl containing trisaccharide in their urine. Studies on the puried enzyme will be used to determine the normal capacity of the liver lysosomes to hydrolyze the alpha-mannosyl glycosides which occur in serum glycoproteins. Experiments will be done to examine the in vivo binding of I125-asialo-fetuin by liver plasma membranes. Five to fifteen minutes after intravenous injection of the radioactive protein, the liver will be removed and homogenized. A purified plasma membrane fraction will be isolated, and the quantity of asialo-protein bound to the liver surface will be determined. In addition, a study will be made to follow the possible entrance of the radioactive protein and/or its degradation products into the bile.